Red mage is the training wheels for raiding. They're useful for learning the fights, but once the raid group has got the mechanics mostly down and are ready to push for kills it's better to have a black mage. It's probably not fair to heavily penalize red mage for that since it's basically just there for learning fights.

But red mage isn't significantly behind summoner as things currently are. It's just that the top half of DPS is way above the bottom half. Though I believe the life letter promised to adjust that, so may be better come end of October.